1. Field of the Invention
The present invention relates to an electrical power unit for increasing the DC power output of an electrical generating system of the type including a DC storage battery and an engine driven alternator which may supply DC power to both the battery and to any load which may be connected thereto. More particularly, the present invention relates to such an electrical power unit which increases the DC power output of the generating system by increasing the AC voltage output of the alternator by using a step down transformer to reduce said voltage to normal system levels. Output of the alternator may be also increased by providing an auxiliary DC voltage of a higher than normal voltage to the field winding of the alternator, independently of the battery. This has the added advantage of making the alternator self exciting, once started.
2. Description of the Prior Art
Modern day, engine-powered land and marine vehicles of many types require that DC power be available at relatively high power levels to supply the many DC powered devices with which they are equipped. Typical examples of vehicles which may require a relatively high DC power supply are boats, ambulances, police cars, fire engines, energy aid units, and the like.
A conventional electrical system for an engine-powered land or marine craft usually includes a DC battery, an alternator adapted to deliver low voltage DC power to the vehicle electrical system and a voltage regulator connected therebetween and adapted to control the voltage output of the alternator in response to the charge variation of the battery. Typical alternators in use today include a stator having three windings connected to provide a three phase AC output and a rotor with a field winding appropriately driven by the engine. Alternators of this type generally include a rectifying circuit adapted to transform the AC voltage to low voltage DC which is then used to charge the vehicle battery and to power the vehicle electrical system and any loads which may be connected thereto.
Other alternators are equipped with terminals by which the alternator's three phase AC output may be tapped directly before rectification and then utilized to provide three phase AC power which can then be employed for many purposes.
It is known to provide auxiliary DC power by modifying the vehicle's electrical system by adding a second or "piggyback" alternator, often mounted adjacent the vehicle's original alternator. The "piggyback" alternator is driven mechanically by belts from the vehicle engine in much the same manner as is the vehicle's original alternator. Such "piggyback" alternators are often difficult and expensive to install due to the often crowded conditions of the vehicle engine compartment. In addition, such a solution to the insufficient power problem involves the added cost of the second alternator, while decreasing overall system reliability by doubling the possibility of a breakdown in the vehicle's electrical systems, since two alternators are, on the average, twice as prone to failure as is a single alternator. As can be appreciated, in all land or marine vehicles reliability is an important criterion which becomes doubly important when the vehicle is used as an emergency, rescue, or police vehicle.
Increasing the size of a conventional alternator to provide all the high DC power requirements which may be needed is a costly solution, and the increased size of such a unit raises the possibility of difficult installation or even lack of adequate room to mount it in the engine compartment.